


Bumpy Ride

by PanPacificPines



Category: Gravity Falls
Genre: F/M, First Time, NSFW, Public Sex, pinecest - Freeform
Language: English
Status: Completed
Published: 2018-09-05
Updated: 2018-09-05
Packaged: 2019-07-07 11:57:25
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,557
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15907809
Author URL: https://archiveofourown.org/users/PanPacificPines/pseuds/PanPacificPines
Summary: Overcrowding sucks. Bus breakdowns suck. Road construction sucks. But somehow, a bumpy as hell, teen-crammed bus ride to school is way better than either of the twins could’ve expected.-Or-When you write porn for your friends and they insist you post it.Oneshot Older teenage Dipper and Mabel discover their shared weirdness on the most memorable bus trip of their lives.





	Bumpy Ride

It was a tuesday, first day back to school after a long weekend.  
"Ugh. Not long enough" was the thought resonating in the bones of every single student returning to school that day. The twins just happened to have an extra dose of that when their bus finally arrived. They'd all heard the rule that if the bus was more than fifteen minutes late, they could go home. Just their luck that it showed up at the fourteen minute mark.  
"Oh shit. Laaaame!" Crowed Mabel. "We could probably just hide, maybe she hasn't seen us yet." The prospect of a free skip day dropped out through the bottom of her day and she wasn't taking it well.  
"I wouldn't count on that....shit. it just got worse though, look." Dipper, motioned for her to take another look.  
"What the hell!? What's going on?" As it pulled to a stop she could see clearly every single seat on their morning bus was full; packed even. As the door slid open the elderly driver, who Mabel was positive must've driven Abraham Lincoln and the western Pioneers to school, gave them their answer.  
"We had three busses break down. Y'all're gonna have to double up. Getcher seats quick-like though."

Mabel grimaced, trying to add up the popularity/social group calculus before the acceleration knocked her over.  
"Butt, turbo Lame. There's no room. What're we supposed to do?" She asked, to no one in particular  
"ya's gonna have to double up'r somethin'. It ain't gonna be forever, now come on an'sit down, we’re late as it is." The front-most seat only had one other occupant. His name was Chad or Brad or something. Begrudgingly he moved his backpack onto his lap.  
"Okay Dip. It looks like we're doubling up." Since he was in front of her anyway, he took the seat and wedged his bag in place just under it.

 

"Well, at least it's just you." She sighed, resigning herself to a cramped, noisy, uncomfortable trip, and plopped down on her brother's lap. Thankfully at least for them, they were the last stop on the pick-up route. And it would just be another twenty minutes until they got to school. So at least they wouldn't have to triple up.

The road, apparently sensing the slight improvement to her mood decided that some fresh road construction would be just what the doctor ordered. The right front tire plowed over a hunk of asphalt just then. It felt like she was thrown into the air, and she would have landed in the aisle if the space weren't so cramped. But Dipper caught her and, eventually their hearts settled down.  
"Hey, can you try to keep me steady, Dip?" She asked, and in response a pair of hands rested on her hips. However, chunks of asphalt don't just appear from nowhere, and a moment later the comparatively smooth ride was replaced with a freshly torn up road.

 

A school bus wasn't the most gentle ride even on the best of days. Theirs transformed into an unbalanced washing machine when it hit that stretch of road. They rattled and shook, and could hear pebbles clinking into the undercarriage as they went. Dipper tightened his grip, practically clamping his twin to his lap. It helped, but the construction crews were tearing up miles of asphalt ahead of them. Even with his hands welded to her sides she seemed unbalanced. Mabel was leaning forward against the barrier in front of them for support since she didn't seem to be able to hold herself up straight after more than a minute of bumps and rumbles.

The ride was making Dipper uncomfortable all around. Of course it was cramped and loud, but having a constant weight pressing into his crotch wasn't helping other matters. He hoped she hadn't noticed and tried to adjust how they were sitting  
"Hey, c'mon Mabes, lean back." He gave a little tug, and she flopped back against him like a ragdoll without resisting.  
"Are you okay?" He asked, forgetting his other concern for a moment.  
"Mmmm- mmhmmm" came her somewhat ragged response. Barry, or Jeff, or whatever his name was popped in his headphones and turned towards the window. Whatever was going on with her wasn't his problem, apparently. But it was rapidly becoming Dipper's. Her legs and back stiffened and she leaned back into his chest, while her butt pressed into his lap. There was no way she wasn't going to notice that.

 

He froze stiff. There was still a possibility that she wouldn't know, or that it was just a fold in his jeans. Until she pressed into it again, sliding herself over the lump. That confirmed it.  
"I-it's not-" he whispered, panicking into her ear.  
"Put your hands back on my hips." She interrupted with a hint of desperation in her voice. Unnerved by the response, Dipper did so immediately,  
"S-sure, sorry." After all, bodies just did things on their own, he knew that, she probably knew that too, he reasoned. And as his mind tangled in a jumble of explanations and excuses, Mabel's body acted. Though she barely needed to do anything with the rumbling beneath them. She ground herself into him, into his lap. He held on for dear life. No one had ever done that to him, much less his twin sister. But the sensation was amazing, and if it worked for her too, he didn't object.

She eagerly gyrated her hips and slid herself across him in every direction. He hoped only they could hear the little sounds she was making, the heavy breathing. He looked around. There must've been fifty people on the bus, and at least two hundred different conversations. Mabel never cared about what people thought, but they were in front of everyone. All it'd take is one person to look over, to notice what they were doing. Hell, Derrick with his headphones in might still realize. But even he was starting not to care. Why hadn't they ever done this before?

Before he could think anything else, the Bus turned off from the construction and up the approach to their school. Conversations changed. Everyone would be clamoring to get off and stretch their legs. If the two of them didn't get themselves together and stand up first, all ten thousand of them would walk past and see.  
"Hey, I think this is our stop" Mabel chirped, seemingly unaffected by what they'd just done. Could it have been his imagination?  
"Yeah, seems that way," he tried. Mabel worked her neck around, then her shoulders, stretching as she did.  
" 'bout time though, right? Jeeze, I thought I was gonna die."  
"Yeah."

Each class seemed to stretch on for days, not that he could remember anything that happened. Dipper's mind was a bit preoccupied. Just as his last class was letting out for the day, though, his phone buzzed in his pocket. He fished it out to check, and found a text from Mabel. She hadn't said anything all day, so he sure wasn't going to. It read "hey, saved you a seat."

His heart skipped a beat when he saw who the message was from, and another when he read it.  
"Calm down, calm down" he commanded himself. Though it was another body part that he was trying to dominate with his will. He didn't stand a chance.

 

There were obviously fewer busses in the parking lot than usual, so they hadn't gotten replacements yet. For some reason, it didn't bother him. Well, aside from all those skipped heartbeats. It was a mystery how he maintained all that blood pressure with that going on every time he thought about his sister. The bus was already half full by the time he made his way onto it. It would've taken him a minute to find her if she hadn't been waving and calling out to him. Mabel was sitting in the farthest back seat on the left, and most of that seat was taken up by an instrument case.  
"Yo, Mabe, what's this? There's no room for me."  
"It's a trumpet or something. French horn? I dunno. I'm just borrowing it from my friend Tracy." Confusion crossed Dipper's expression, but he learned years ago to deal with that emotion around his twin.  
"You're borrowing it even though you don't know what it is?" She scooted herself out, along with the instrument case and beckoned him to sit towards the window.  
"Yup. Don't worry about it." He shrugged and slid in and followed her lead.

 

Dipper's internal assumptions were thankfully confirmed for him when Mabel did the 'movie theatre scoot' in front of him and blocked off the rest of the seat with the case and their backpacks. The shoulder straps were hooked in the crook of her arm. Then she took up her seat in his lap with a playful wiggle of the hips. But she surprised him again with how cool she played it. Above the barrier of theirs, she was just regular Mabel, chatting with him about nothing, but filling what would have been silence with the sheer force of her personality. But where no one could see, she'd give him a more than playful shift of her weight.

 

The bus was packed full a few minutes later. A short while after that the fleet moved out, lining up to pull onto the main road. By then no one was much paying attention to the twins. Mabel's demeanor shifted; only Dipper could've ever noticed. She stood very slightly and snaked a hand between them, dragging his zipper down. She caressed him through the opening, aiming him in the right direction before taking her seat again. He did all he could to keep his face straight through it all. She smirked back at him and began slowly tugging her skirt up, pulling it between them. He had to bite his lip to keep from shuddering. He didn't succeed entirely, but no one seemed to notice. Or at least they didn't care. 

 

There was barely anything in between them physically. And just that morning, before they got on this very same bus they had been brother and sister; as close as they thought they ever could have been. He was entirely and profoundly wrong. With Mabel's skirt hiked up, the only thing in their way were a couple pairs of underwear. He could feel the slick moisture of hers as she slid herself over him. His body, almost without his urging it, pushed upwards into her.

 

His mind raced, dozens of thoughts firing off at once. She changed in the hours they were apart, transformed into someone else; and it was getting to him too. She wasn't just his sister anymore. Dipper had never been more excited, more turned on by another person. She didn't fit the same space in the world anymore. Before she was ‘Only Mabel’. Just that morning her body was only just that. But now? She was different. He was different too, but her hips, the curves of her body, her neck… he wanted every part of her like never before. 

 

And Mabel immediately seized what she wanted. She had band class in first period. So either she had been carrying that thing around all day, or else just been thinking about it that long. She made a plan, followed through with it, and got what she wanted. And his compliance either wasn't a factor, or she knew damn well he'd give it to her. He wanted her, needed her. 

 

Then the bus clattered suddenly back onto the uneven paving. Dipper immediately wrapped his arms tight around Mabel's waist, holding her in place. Their bodies, along with everyone else's, vibrated. But their's vibrated together. Mabel clenched her teeth to keep from moaning, pushing into the seat in front for for support. Her twin rattled beneath her, putting her massaging shower head to shame (well, almost). Dipper’s embrace made her feel secure. 

They were given a brief reprieve when the driver pulled up to drop off the first batch of riders. When she came to grips with her surroundings she took in the unfamiliar view out the window. And while quite a few others had left the back, the seat in front of them was still occupied, and one of the girls in front of them was grimacing at her.  
“You're pushing on my seat. Are you, like, okay?” she sneered.  
“Oh!” Mabel let up her grip. “Sorry! I get real bad motion sickness. I was trying not to- Huhhnnnggg” her eyes rolled back for half a second as she seemed almost about to heave before regaining composure. She laughed nervously, “S-sorry about that! I'm probably f-Fine now.”  
The two girls made horrified expressions and ducked down in their seat, obviously hoping to be able to change seats soon. 

 

Mabel pinched her brother's thigh. She'd rolled with it, but his decision to roll his hips and press into her clit nearly made her lose her composure. Dipper chuckled slightly and whispered softly,  
“Sorry. Couldn't help it.”  
She responded by running her nails across his leg in a conciliatory gesture before wriggling her butt firmly into him. His grip tensed as the bus rattled on down the road and he moaned a low hum into the back of her neck. By then they’d already stretched the limits of what fabric could contain. The part in Dipper’s underwear was threatening to loose him at any moment. Some other hypothetical Dipper could worry about that. At that moment all either of them could think about is how good they felt. 

 

They clattered along past a few more bus stops. The back of the bus emptied out quickly. The threat of motion sickness probably helped. The girls that had been sitting in front of them were both gone. One got out at her stop, but the other simply moved to a different seat. The back half of the bus was fairly sparsely populated, but the last three rows belonged only to them. Mabel was feeling bold. She leaned into her grinding some more, only easing up during stops. She turned her head to speak. It wasn't a whisper; she just lowered her voice so only he could hear. 

“Having a good time?” she purred. He attempted a response, but only managed a groan at first.  
“Hnnggg...Oh my god Mabes,” he gasped.  
“Did you want me to stop?” a small hint of concern colored her voice. He paused to think, taking in their situation, and the new paradigm of their relationship.  
“Fuck no. But I wanna talk about it later, okay?” Dipper kissed the back of his sister's neck.  
“Mmmm, tingly” she giggled, “okay. It's a deal. Love you, bro.” He could practically see the little heart emojis floating around the words that her inflection put there.  
“Love you too” he smiled, contentedly leaning his forehead into the base of her neck.

 

Interrupting his reverie, since they were on smooth road again, Mabel slithered a hand between their legs and freed him from the gap in his undies. He seemed to swell in her grip. She ran her thumb over the back of the head, savoring the shudder reverberating through her back. As she parted her panties to one side and rubbed him against her slick wetness manually. She couldn't believe it'd taken them so long to try this. Her body greedily ground back into him. She had a toy back home, bought online with a gift card and hidden in her room, but she would gladly replace it with her twin. Mabel allowed herself a low, throaty groan. She bet he fit perfectly inside of her. 

 

She got her answer moments later when the bus hit a bump in the road and he slipped from her grip. They both let out a sharp yelp of surprise. There were a few turned heads, but when the twins failed to entertain further, they were ignored again.  
“Dipper!” Mabel gasped under her breath the moment no one was looking. The tires clattered across a few more bumps. Mabel sank down entirely around her brother. She could've believed the driver was hitting every bit of debris on purpose.  
“Sorry, I didn't mean to” panted Dipper as he started lifting her off of him. 

 

Even as he did, she rolled herself into him again, allowing her body to take him deep once more. His grip slackened and she leaned her arms and forehead against the empty seat in front.  
“M-mabel-!” All their bags were allowed to slump to the floor. She didn't care who else was around or where they were.  
“our stop-” Her hips pumped Inexpertly but eagerly. Mabel bottomed herself out onto him again and again. Dipper patted her insistently. He was trying to say something.  
“I'm-” he panted. She wasn't slowing down. “Oh fuck, I'm- Mabel, our stop is next- I- oh fuck-!” more, she needed just a little more. She was so close. 

 

Dipper sensed he wasn't getting through to her and was slightly panicked. Their stop was next. He squeezed her breast to get her attention, trying his best to guess where her nipple was. She bit down onto the sleeve of her sweater as a shuddering moan escaped. Her entire body quivered in his lap, and the hot, urgent feeling in his belly was too much to ignore. Her body bucked, sliding around him again and it was too much to take. Using all his strength and willpower he lifted his sister off of himself and shot the last of his stamina into the folds of her skirt. It was only then that she peeked back at their surroundings.  
“Jizznuggets! That's our stop!” 

 

Mabel hopped over onto the seat and quickly adjusted herself. She patted down her hair, straightened her skirt and panties to make sure it all sat properly. The brakes hissed and the slight feeling of everything falling forward one last time rose through her belly. Her legs were still trembling, but she could deal with that. They gathered up their bags and Mabel gave one final scan of her brother and caught his fly down.  
“Dip! XYZ, Come on!” she whispered. Shock and terror danced in his eyes for half a moment before nodding his thanks and zipping himself up. Their hearts raced as they trudged down the aisle one after the other, hoping they'd been low key enough. Just to be sure, Mabel forced herself to walk slower than she wanted to, hunched over as though she were carefully cradling her stomach. It seemed to work since disgusted girl number one held her bag up like a shield.

 

The door creaked shut behind them and the massive engine roared to life again as it headed off down the road. Nobody shouted out the windows at them, so the twins shared a sigh of relief before really looking each other in the eyes for the first time since everything had changed between them. They shared an identical blush. Dipper cast a glance around the neighborhood, finding their cul de sac empty.  
“So...we just did that, huh?”  
“Any regrets?” Mabel asked, her heart beating in her head. He smiled from ear to ear.  
“Uh, maybe the execution, but otherwise? N-” her lips crashed into his, wrapping her arms around his neck. 

 

None of their neighbors were outside. Thankfully for them most of them weren't even home from work because it took the twins quite some time before they surfaced for air. Stars twinkled in Mabel's eyes.  
“Can we do it again?” He looked shocked that she would even ask.  
“I might need a juice box and a snack, but hell yeah. Did you think I'd say no?” She stuck her tongue out and licked the tip of his nose.  
“Nah. Pretty sure you're...hey...are you my boyfriend now?” despite what they'd just done her blush deepened. He held her around the waist and smiled.  
“Yes. Definitely. Absolutely.”  
“Awww yis. Which is good, cuz you gotta take responsibility for this.” Mabel took a step back and lifted her skirt up, flashing her thighs and panties. Her panties were just a little more pink since her thighs were starting to pale again around the sides. But it was probably the extra large, globby stain on the underside of her skirt that she meant to draw his attention to. Though he noticed that last. 

 

“Hey, hey, put that away.” He chuckled, adding a moment later “until we get inside at least.”  
“What's wrong, Dipper?” She mocked with a silly voice, “don't you love us!?” Mabel held the blob as close to his face as she could get. He rolled his eyes and pushed her away.  
“Okay, okay. That's enough of that.”  
“Give us a kiss!” she shot back in the same voice.  
“Oh no. I'm not gonna do that. You're gonna have to let me work up my courage before I do that.”  
“Oh, good to know, I'll remember that.” Mabel giggled, moving back in close. With half-lidded eyes she intoned “just so you know, I don't need to work up my courage. “ before licking her lips. “Oh, hey, look who's ready to go again.” Dipper practically carried her and all of her luggage home, grateful to have the next few hours to themselves.

**Author's Note:**

> As always, feel free to let me know what you think, and I hope you enjoy it.


End file.
